A communication between a field device and a control system in a process control system progresses to a wireless represented by a wireless communication standard ISA100.11a for an industrial automation which is determined by an ISA100 committee of an international learned society of instrumentation control (ISA: International Society of Automation) and issued in September, 2009 via a hybrid communication such as HART (a registered trademark) that a digital signal is superimposed on an analog communication of 4 to 20 mA and a digital communication such as FOUNDATION Fieldbus (a registered trademark) or PROFIBUS (a registered trademark) from an analog communication of 4 to 20 mA by a two-wire type signal wire.
By the hybrid communication or the digital communication, a quantity of information that can be used by a plant operation is outstandingly actively increased. As a result, versatile information such as a plurality of process quantities or diagnosis results which are transmitted by devices can be sent to a host system such as a DCS (Distributed Control System) or a device management system, so that facilities can be managed, previewed and maintained.
A field wireless technology that makes the communication between the field device and the control system wireless has many merits, in addition to the above-described merits, for instance, a wiring or an engineering cost can be reduced, devices can be installed in places where the wiring is difficult, and the devices are easily added or removed. Thus, when the above-described merits are put to practical use, it is possible to anticipate a realization of an instrumentation which has been impossible so far.
When the process control system based on the ISA100.11a is formed, a field wireless management station in which a gateway function and a system management function are incorporated is made to be redundant.
FIG. 6 is an explanatory view of a structure which shows an example of a conventional redundant connection of the field wireless management station. In FIG. 6, the field wireless management stations 11 and 12 have the gateway functions and the system management functions incorporated. Main modules 11a and 12a and switch modules 11b and 12b are shown which are provided to realize these functions.
The field wireless management stations 11 and 12 are connected to a host network NW1 and connected to a synchronizing network NW2 to take synchronization between the field wireless management stations, and further connected to a backbone network NW3 including four layer-2-switches SW1 to SW4 which are connected together in the form of a loop to connect backbone routers 21 and 22 thereto.
Thus, the field wireless management stations 11 and 12 and the backbone routers 21 and 22 are respectively formed to be redundant.
Here, the four layer-2-switches SW1 to SW4 connected together in the form of the loop which form the backbone network NW3 can open an arbitrary port in accordance with, for instance, an RSTP (rapid spanning tree protocol).
Accordingly, for instance, when a communication trouble occurs due to a failure of any of the ports of the layer-2-switches, the failed port may be selectively opened and bypassed to continuously carry out a communication.